Thirteen years ago a sidecar outfit powered by a
BMW flat twin won the FIM World Sidecar Championship. It was not the Bayerishce
Motoren Werke's first appearance in championship colors, for the factory's
supercharged twins had been strong contenders in prewar racing, winning the
senior solo championship in 1938. What was to be important about that 1954
victory was its initiation of an uninterrupted series of class championships
which continues to this day. For thirteen years BMW has held the sidecar crown,
and for twelve years it has been marketing its "sidecar" production motorcycle,
the model R60.

In an era of rapid technological change, one
might reasonably ask how any motor company could successfully sell the same
model for 12 years, especially when the sidecars that model was meant to haul
have virtually disappeared from the world's highways. The reasonable answer to
that question is complex, for the idiosyncratic mind of the motorcyclist is not
about to lend itself to uncomplicated explanations. But we might begin by
looking at this month's test R60 for characteristics that prove useful in a
solo.

The sidecar outfit was once a sort of poor man's
car. A man could buy an inexpensive (by auto standards) motorcycle, ride it solo
until he had saved up enough to add a sidecar, then take the wife and kids along
with him. Over-all investment would still be less than for an automobile, and
running costs considerably less. Well, mass production changed that idea almost
before it got off the ground. "Basic transportation" in an automobile has for
some time been cheaper than a good sidecar rig with comparable performance.

Other than power, what the sidecar man needs from
his engine is high torque and good but not abrupt engine braking. He prefers a
reliable, mildly tuned engine over a peaky, temperamental scorcher. Cooling
characteristics have to be very good, for a sidecar rig is heavy, has lower
gearing, and gets less cooling air at a given rpm than a solo. Owing to the way
a chair corners, the engine needs a pronounced flywheel effect to keep power
delivery smooth and to prevent wild overreving during wheel breakWay in power
slides. Also important is carburetion that does not lean out under horizontal
g-loads in cornering. For best stability as well as minimum wind resistance, the
sidecarist prefers an engine with a low height and center of gravity, permitting
the outfit to lie close to the ground.

Most of these requirements can be quite useful in
a solo bike, depending on one's riding habits. And apparently the R60 suits the
riding habits of quite a few for it is the most widely sold BMW in the U.S. A
heavy flywheel does contribute to smooth engine output, especially if the firing
pulses are even and if the engine's reciprocating masses (pistons, con-rods
etc.) are balanced against one another—as they are in the horizontally-opposed
R60 powerplant. Low center of gravity helps the handling of any motorcycle. And
mild tuning combined with the frame rigidity necessary for a sidecar make for an
extraordinary reliable and robust unit.

Most of our readers are already familiar with the
basic BMW layout; it has been around in the R60 for 12 years and in other models
since 1923, a year after Master engineer Max Friz of Munich conceived it. The
horizontally opposed engine, its crank aligned with the fore-and-aft axis of the
bike, couples through an engine-speed clutch to an in-unit gearbox at the rear.
From the gearbox, a universal joint, shaft, and bevel gears, carry the drive to
the rear wheel.

We have known serious motorcyclists in moments of
cynicism to remark, "The BMW represents a triumph of development over design."
Let us now examine a few developmental details that might inspire such a remark.
The BMW is packed with particulars of great ingenuity and high manufacturing
skill.

The engine, for example, gets its intake air from
two sources. The first is through the centrally mounted air filter, which feeds
both carburetors through a common chamber via separate tubes. The second intake
is by way of small vents in the nose cover on the engine unit. Under this cover
sit the magneto, braker points, capacitor, generator and voltage regulator.
Intake air passes over these components, keeps them considerably cooler than
crankcase temperature, then passes through a crankcase passage, another air
filter, and into the common chamber under the main air filter.

The electrics, made by Bosch of Germany are a bit
old-fashioned by present standards, but in the BMW they are far more reliable
than the components commonly fitted to other bikes. The 60-watt DC generator
puts out an actual 90 watts at any crank-speed over 1700 rpm. The magneto is
mounted on the end of the camshaft and turns at half engine speed. The braker
cam has two lobes, thus opening the points once per crank revolution. This
magneto is completely independent of the generator-battery system. Starting is
invariably a one-kick job, and the bike can be driven safely, even at night,
with a dead battery. The electrics are also completely water proof—mostly
undercover and carefully protected.

Behind the enclosure for the magneto and
generator is another cover for timing gears. A large gear mounted on the crank
drives a gear for the camshaft and a gear to oil pump. A continuous oil stream
plays out of a jet into the meshing of the mainshaft-camshaft gears. These have
been individually selected and fit at the factory down to the exact size of each
crankcase housing, and there is only .0005 inch of backlash. The mainshaft gear
also carries a flat plate with cutaways that precisely time crankcase breathing.
The cutaways alternately open and cover vents to the crankcase much like the
rotary intake valves on modern two-strokes.

The crankshaft itself is a hefty built-up (or
pressed together) unit with large roller bearings at the connecting-rod lower
ends. The crank turns in two roller-type mainbearings. The lack of a central
main-bearing means some crank flexing at higher rpm, but this does not become a
serious problem within the R60's rev limit of 6200 rpm. Seen from above, the
cylinders are slightly offset, creating a rocking movement about an axis
perpendicular to the plane of the cylinders. Not only is this slight, but it is
well damped by the R60's frame. In dynamic terms, the horizontally-opposed flat
twin is the best balanced of any of the common motorcycle configurations. In the
R60, this is felt as extraordinary smoothness and virtually vibration-free
operation throughout the power band. With its 7.5:1 compression ratio and
conservative valve timing, the R60 is also very tractable with strong pulling
power (torque over 26 ft-lb.) anywhere above 2500 rpm.

Although the solo R60 used the same
single-dry-plate clutch as the sidecar unit, it has a gearbox and rear drive
with taller ratios. At maximum torque in fourth gear (4200 rpm), the R60 is
rolling along at 65 mph, a very smooth and comfortable cruising speed that
consumes just a shade under 50 miles per gallon of regular gas. The engine will
not quite pull maximum power in fourth gear, which at 6000 rpm and 32 bhp would
be 92 mph. Instead, it rises to a steady 5800, or 86 mph, and stays there.

Some nice touches in gearbox construction are
hard-chromed shifter-fork tips for longer wear, a clutch throw-out bearing
running in transmission oil, and gearbox venting to the atmosphere through a
small hole in the speedometer drive. The speedometer drive gear has been
designed with an extra return spiral that sends any condensed oil vapor back to
the gearbox rather than out the breather hole. Result, a clean gearbox that
rarely blows its oil seals. The only disadvantage to this gearbox: its input
shaft runs at engine speed. A heavy flywheel keeps that engine from changing
speed too quickly and often delivers quite hefty jolts to the input shaft on
gear changing. Consequently, a spring-and-cam type torque damper is fitted to
the input shaft. This protects the gears from the engine side, though the
necessity of running two offset shafts for the gear pairs is less efficient
mechanically than the more conventional arrangement of two shafts total.

Protection from wheel-delivered shocks is
provided partially by the drive shaft itself, which permits a slight amount of
both lengthwise and torsional flex. Normal change of length required by movement
of the rear suspension is provided by a sliding splined-cup joint at the rear of
the shaft. An elaborate linkage to the rear brake arm also keeps an even braking
tension on that arm despite vertical movement on the rear wheel.

Counting the rear drive unit, the R60 has four
separate oil enclosures, each of which must be sealed off from the others. There
is the crankcase and wet sump, the transmissions. The universal joint and shaft
drive, plus the rear drive. Virtually every rotating load-carry surface within
this series runs on roller or ball bearings and all receive a generous oil bath.
Again, a good case for lengevity. The only possible catch is maintaining all
those oil seals.

Every enclosure but the shaft drive housing is
adequately vented and part of the latter is a neoprene expansion boot over the
universal joint. This offers enough low-resistance expansion volume to obviate
positive venting.

The frame through which this power train passes
is basically a sidecar frame. That means it's strong and heavy. BMW uses all
kinds of tricks in the basic double-loop cradle, such as varying cross sections
at different points according to load. Much of the tubing, oval sectioned and
tapered, is very expensive to fabricate. Helmut Kern, service manager at Butler
and Smith, the U.S. importers of BMW says, "As far as I know this is the only
frame that you can hook a sidecar to, and later ride solo. Any other frame I've
tried will eventually distort under the loads imposed by the sidecar, throwing
it out of alignment for solo work."

Another vestigial sidecar component that benefits
the solo rider are the R60's brakes. The sidecars BMW made (but no longer make)
had a brake in the wheel, but many machines were fitted by owners with less
expensive, brakeless rigs.

This meant that the bike's brakes did all the
work, which might be hauling a 1400-1b. package to a standstill from 65 mph. It
is not surprising that BMW was the first firm to fit full-width brake hubs on
all production motorcycles. They were also among the first to use a
double-leading-shoe brake at the front. Twelve years ago these brakes paced the
industry and were undoubtedly the best production stoppers available. They are
still above average for large-displacement bikes, but technology has caught up
with, and in some cases, passed BMW. Our specific brake loading figures show
what our riding experience confirms: The R60 has good brakes, but they could be
better for such a large machine.

Up front the R60 also features one of the most
unique forks in the motorcycle industry. A full Earles-type leading-link fork,
it has both advantages and disadvantages compared to the more common telescopic
variety. Like so much else on the BMW, the fork is both heavy and strong. It was
ball-and-cone bearings at the steering head and taper-rollers at the swingarm
pivot. Under heavy braking, the swingarms want to turn forward about the pivot,
effectively raising the bike. At the same time momentum transfers most of the
weight of the bike and its rider forward, forcing the front end down and
swingarms backWard. The effects are self-cancelling, and the BMW brakes very
evenly without nosedive or lifting.

The rear swingarm of the BMW also pivots on
tapered roller bearings. Its suspension units are the conventional coil-spring
and shock-absorber combination, but they are secured at the top in housings
welded to the rear of the frame loops. The pivot points are located in two
vertical members connecting the lower and upper cradle sections. This
arrangement does not offer best resistance to side loads at the wheel and we
experienced what felt like flexing during hard cornering with two up.

Our test of the R60 was rather more thorough than
most road tests, for not only did we run it at the track, we also drove it 1400
miles from New York to Daytona. BMW has produced some 250,000 motorcycles since
World War II, and they gave us our test bike to celebrate the fact. It was
completely stock, we drove it hard, and we experienced no mechanical
difficulties. There was some sweating at the vertical crankcase joints, but no
.oil leakage and virtually no oil consumption.

The R60 is most at home on the open highway,
where it will cruise smoothly at 65 or 70 for day after day almost without end.
It is a big machine, almost overdesigned and certainly overbuilt for a solo
mount. Such a "utility" orientation makes the R60, not surprisingly, the largest
selling police motorcycle in the world. But utility demands good manners,
strength, and durability. The R60 exhaust note is low and mellow, emerging from
an interconnected twin-pipe, twin muffler system. Workmanship, fitting,
finishing —all are superb. Buyers have an option of various seats, tanks,
handlebars and racks. Ours had the solo seat, which is quite comfortable, but
far too low for the high "touring" bars fitted.

The R60 is certainly no road sports machine. It
will do zero to 60 in a shade over 16 seconds, and third gear will carry you to
about 78 mph for brisk passing. But the combination of 440 lbs., 30 bhp, and a
heavy flywheel doesn't make for neck-snapping acceleration, or ear-holing at
high speed through a series of left and right hand switchbacks. That heavy front
end and over-all weight just can't be thrown back and forth quick enough for
hard tight-course riding. This is a machine for long distances, for a
comfortable, trouble-free ride, for the rider who wants more to see the country
he's passing through than to explore the limits of his cornering and braking
skill.

Routine servicing of the BMW is easy. All the oil
reservoirs are readily tapped, the electrics can be reached by undoing two
bolts, and the valve gear, pistons, cylinders and carburetors hang right out
there for ready service and adjustment. Naturally, there is no "greasy chain" to
fuss with. In contrast, power-train servicing is a nightmare. Lower end,
transmission, drive shaft, and rear drive overhauls require more special
pullers, drifts, jigs, wrenches, holders, and fixtures than one can imagine,
much less afford. And breaking the power train to service it is a lengthy,
exasperating job. Fortunately, for BMW owners, the R60 is built to last, and we
know one chap who has 270,000 miles on his bike without ever having so much as
removed a cylinder head.

Ironically, as history's clock has caught up with
and passed BMW, there has been a recent resurgence of interest in sidecars. The
R60 may once again serve for a limited few its original task. Butler and Smith
now markets Dutch-made single-passenger sidecars under the BMW marque.
Meanwhile, the factory has been blossoming financially under the demand for its
automobiles and is completing a new facility for motorcycle manufacture.
Although now said to the point of weariness, the near future may bring new
models and more modern designs from BMW. Meanwhile, the R60 will continue to do
its workhorse chores with the characteristic stamina and unfaltering good
manners, that have made it a favorite of long-distance touring riders.

Source Cycle Magazine

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